Switching the perpendicular magnetization of a magnetic insulator by magnon transfer torque

Magnon transfer torque (MTT) is regarded as capable of manipulating spin by magnons or spin waves only without spatial movement of electrons, which is a key to enrich the toolbox for magnonics. Here using a magnon current through an antiferromagnetic NiO spacer, which can be deep into a magnetic insulator ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YIG), we demonstrated the perpendicular magnetization of the YIG in a YIG/NiO/Pt heterostructure could be switched. When the thickness of the magnon channel NiO was 1.5 nm, the magnon current could still maintain about $84\%$ of the spin current for the YIG/Pt control device, indicating high efficiency of the NiO spacer in transferring magnon torque. Switching the perpendicular magnetization in the YIG/NiO/Pt heterostructures unambiguously verified the effect of magnon transfer torque (MTT), which may advance the development of magnonic memories and logics.

Figure 1

Characterization of the perpendicular YIG/NiO/Pt structure. (a) Schematic diagram of the MTT effect in the structure. (b) Image of a patterned YIG(5.0)/NiO(1.5)/Pt(3.0 nm) Hall bar device. The current was applied along the $x$ axis and the anomalous Hall voltage was picked up along the $y$ axis. (c) The cross-sectional high-resolution TEM image of the YSGG//YIG(5.0)/NiO(1.5)/Pt(3.0 nm) structure. The inset shows the FFT pattern of the substrate. (d) The cross-sectional HAADF-STEM image of the same structure. [(e)–(g)] The corresponding energy dispersive x-ray (EDS) mapping of different elements.

Figure 2

AHE and SMR of the YIG/NiO/Pt structure. (a) In-plane and out-of-plane magnetic hysteresis loops of the YSGG//YIG(5.0)/NiO(1.5)/Pt(3.0 nm) structure measured by VSM at 150 K. (b) Anomalous Hall resistance of the YSGG//YIG(5.0)/NiO(1.5)/Pt(3.0 nm) Hall bar device as a function of the out-of-plane ($H_z$) and in-plane magnetic field ($H_x$). [(c) and (d)] Angular dependence of magnetoresistance of the YIG(5.0)/NiO(1.5)/Pt(3.0 nm) and the YIG(5.0)/NiO(25)/Pt(3.0 nm) structures, respectively. The illustrations in (d) correspond to definitions of different angles. All data were measured at 150 K.

Figure 3

Perpendicular magnetization switching driven by MTT in the perpendicular YIG/NiO/Pt structure. [(a) and (b)] The dependence of $R_{xy}$ on switching current for YIG(5.0)/NiO(1.5)/Pt(3.0 nm) and YIG(5.0)/NiO(1.0)/Pt(3.0 nm), respectively, under different bias fields $H_x$. [(c) and (d)] The dependence of the critical switching current on $H_x$ for the two devices ($t_{\mathrm{NiO}}=1.5$ and 1.0 nm). All data were measured at 150 K.

Figure 4

Determination of the blocking temperature. (a) $R_{xy}\text{−}{H}_z$ curves at different temperatures vs the exchange bias. (b) Exchange bias field of the YIG(5.0)/NiO(1.5)/Pt(3.0 nm) obtained from the $\mathrm{\Delta }{R}_{xy}\text{−}{H}_z$ curves for different temperatures in (a). (c) $\mathrm{\Delta }{R}_{xy}\text{−}{H}_z$ curves of YIG(5.0)/NiO(1.5)/Pt(3.0 nm) under 150 K.

Figure 5

AHE and MTT switching behaviors for different control samples. (a) $\mathrm{\Delta }{R}_{xy}$ measurements for the YIG/MgO(1.0 nm)/Pt, NiO(1.0 nm)/Pt, YIG/NiO(1.0 nm)/Pt, and YIG/NiO(25 nm)/Pt samples. [(b)–(d)] AHE and MTT-induced magnetization switching curves at $H_x=100$ Oe for the YIG/$\mathrm{NiO}(t_{\mathrm{NiO}}$)/Pt samples with $t_{\mathrm{NiO}}$ = 0, 2.0, and 3.0 nm. Corresponding $H_z$ dependence of $\mathrm{\Delta }{R}_{xy}$ are also shown. For $t_{\mathrm{NiO}}$ = 0, MTT switching was observed with $H_x$ changing the switching direction on the basis of a parabolic background due to current-induced heating. For $t_{\mathrm{NiO}}$ = 2.0 and 3.0 nm, AHE due to the SMR effect was observed. However, MTT switching was absent for the two samples. All data were measured at 150 K.